1. Field of the Invention
The present invention relates to an electron collector for an electron beam tube, and more particularly to such electron collectors that are liquid cooled in a space efficient manner and provide superior operating characteristics.
2. Description of the Prior Art
Electron beam tube devices, such as traveling-wave tubes (TWTs), klystrons and the like are in wide spread use in many different technologies. Such electron beam tube devices conventionally possess four basic elements, namely an electron gun, an RF interaction circuit, a magnetic electron-beam focusing system and a collector. The function of the collector is to collect the electron beam, after it has passed through the interaction circuit, and dissipate the remaining beam energy. As the electron beam passes through the interaction circuit, the electron beam typically loses various amounts of energy. However, an electron beam typically maintains more than half of its original energy as the electron beam impinges upon the collector. The absorption of the electron bombardment by the collector causes the collector to heat, thereby requiring the collector to be cooled.
The overall efficiency of many electron beam tube devices can be increased by operating the collector at a voltage lower than the electron beam voltage. Such collectors are known in the art as "depressed collectors". Depressed collectors introduce a potential difference between the interaction circuit and the collector. However, in a single-stage collector the amount by which the collector can be depressed is limited by the energy of the electron beam impinging upon the collector. The potential drop between the interaction circuit and the collector can be no greater than the amount of energy possessed by the slowest electrons contained within the electron beam, otherwise the electrons will be turned away from the collector and re-enter the interaction structure, causing oscillations.
The efficiency of an electron beam tube device can be further increased by introducing multiple depressed-collector stages. Multiple collector stages allow for the collection of the lowest energy electrons at one stage, while allowing those with more energy to be collected at secondary stages that are depressed at a higher bias. Consequently, the degree by which the collector can be depressed is not as severely limited by the energy of the electron beam, as in a single-stage collector.
When electron tube devices are miniaturized to fit certain applications, the electron collectors are also miniaturized. With a miniaturized electron collector, there is not much space available that can be dedicated to heat sinks or heat exchanges. Consequently, to prevent overheating of the collector or to prevent the collector from causing adjacent electronic components to overheat, the power dissipated by the collector is limited so as to not exceed the thermal capacity of the overall system. It will therefore be understood that by actively cooling the collector, the collector can dissipate greater amounts of heat and the electron beam tube device can run in higher power applications and at higher efficiencies. One of the most efficient ways to actively cool a collector is through the use of a liquid coolant. However, conventional liquid cooling schemes are not space efficient and are therefore not readily adapted to miniaturized applications.
In U.S. Pat. No. 3,260,885 to Crapuchettes, entitled ANODE STRUCTURES PROVIDING IMPROVED COOLING FOR ELECTRON DISCHARGE DEVICES, a collector is described wherein a single helical coolant pathway is formed around the periphery of a metal collector element. A coolant liquid is pumped through the coolant pathway thereby cooling the collector element. Since the collector element is a single metal piece, the collector element acts as a single stage collector and does not embody the advantages of a multi-stage depressed collector. Furthermore, since the coolant follows only a single path around the collector element, the coolant must be rapidly pumped through the coolant pathway in order to adequately cool the collector element, and prevent the coolant from overheating. Lastly, the creation of a helical coolant pathway around a collector element is very difficult, especially if the collector is a miniaturized component.
U.S. Pat. No. 3,970,891 to Heynisch et al, entitled ELECTRON COLLECTOR FOR AN ELECTRON BEAM TUBE and U.S. Pat. No. 3,388,281 to Arnaud, entitled ELECTRON BEAM TUBE HAVING A COLLECTOR ELECTRODE INSULATIVELY SUPPORTED BY A COOLING CHAMBER, both show collectors having coolant chambers formed around the periphery of the collector. In both patents, the presence of the coolant chamber adds significantly to the size of the collector device, therefore making the collector element impractical for many miniaturized applications.
In Russian Patent 656127, a collector is described having tubing wrapped around the exterior of the collector body. Coolant is pumped through the tubing cooling the collector. The tubing adds to the size of the overall collector, therefore making the collector impractical for many miniaturized applications. Furthermore, the coolant tubes are on the exterior of the collector. As such heat must travel across the entire width of the collector before it can be absorbed by the coolant.
In each of the prior art patents set forth above, the collectors described are single-stage collectors having a single set electrode design. None of the patents disclose a multi-stage depressed collector or a collector with a flexible electrode design. When a collector is designed for a given application, the theoretical design usually requires several experimental iterations before the collector is properly matched to the application. As such, there exists a need in the prior art for a multi-staged collector that has a flexible design and can be selectively altered into several internal electrode configurations. Furthermore, the need exists for such a flexible multi-staged collector that is liquid cooled in a manner that dissipates a large amount of heat without occupying a large amount of space.
It is therefore an objective of the present invention to provide an electron beam tube collector that can be selectively altered to include any number of depressed stages and includes a liquid cooling construction that removes large amounts of heat from the collector without significantly adding to the size of the collector.
It is also an objective of the present invention to provide a electron beam tube collector that is easier to manufacture, is more reliable and operates at higher temperatures than comparable prior art collectors of an equal size.